Spin logic device, also known as magnetic logic device, is a kind of logic device that is formed with magnetic materials and operates by using electron spin characteristics of the magnetic materials. When compared to traditional semiconductor logic devices, this spin-polarized transport based logic device has such advantages as high operating frequency, infinite times of reconfiguration, non-volatility of logic data, radiation resistance, compatibility with Magnetic Random Access Memories (MRAMs), etc., and thus it is considered as a promising candidate for the next generation logic devices that substitutes the traditional semiconductor logic devices.
FIG. 1 shows a prior art spin logic device 100. As shown in FIG. 1, the spin logic device 100 includes a so-called magnetic tunnel junction MTJ core unit that has two ferromagnetic layers FM1 and FM2 with an insulating barrier layer I interposed therebetween. Three input lines A, B and C are provided over the magnetic tunnel junction MTJ, and two output lines Out are provided on upper and lower sides of the magnetic tunnel junction MTJ, respectively. The two ferromagnetic layers FM1 and FM2 of the magnetic tunnel junction MTJ may have different coercive forces, and the three input lines A, B and C each may be provided with an input current of the same level. When only one of the three input lines, for example, the input line A, is provided with the input current, neither the ferromagnetic layer FM1 nor the ferromagnetic layer FM2 will have its magnetization reversed. When two of the three input lines, for example, the input lines A and B, are provided with the input current in the same direction, one of the ferromagnetic layers FM1 and FM2 that has a lower coercive force will have its magnetization reversed, while the other will not. When each of the three input lines A, B and C is provided with the input current in the same direction, both ferromagnetic layers FM1 and FM2 will have their magnetization reversed. Therefore, the MTJ may be configured into 4 different initial states among which two are parallel states where the ferromagnetic layers FM1, FM2 have magnetizations parallel with each other and two are anti-parallel states where the ferromagnetic layers FM1, FM2 have magnetizations anti-parallel with each other. In the parallel states, the magnetic tunnel junction MTJ has a lower resistance; while in the antiparallel states, the magnetic tunnel junction MTJ has a higher resistance. As such, a plurality of different logic states may be achieved. The operation of the magnetic logic device generally includes two steps. The first is a resetting step to place the magnetic tunnel junction MTJ into a predetermined initial state by activating one or more of the input lines. The second is a logic operation step to apply an input current on one or two of the input lines and then or simultaneously read out resistance (or voltage, current) of the MTJ by applying a reading current between the two output lines.
Unfortunately, the prior art spin logic device 100 of FIG. 1 has several shortcomings. For example, it contains too many wirings and thus a very complex structure such that the manufacture thereof faces many challenges. In addition, since the spin logic device 100 relies completely on the Oersted field generated by a current passing through the input lines to reverse magnetization of the ferromagnetic layers, it has to use a large current in order to generate an Oersted field strong enough to reverse the magnetization, leading to high power consumption. These shortcomings have obstructed the practical application of the prior art spin logic devices in modern electronics equipments.